Correct diskused and files when cloning a volume

Correct diskused and files when cloning a volume

Recalculates a volume's disk space used and number of files upon
every clone where it is effortless. Even though tracked mostly
correctly, bugs and accidents leave their traces which only a
salvage would correct.

Change-Id: Ied6fb9eb3944b6e30eac175fe42649c5b7cfaefb
Reviewed-on: http://gerrit.openafs.org/756
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-on: http://gerrit.openafs.org/975